Before you read this, I want to make it clear that these methods were obtained from the Elite: Dangerous community and I, in no part, am responsible. People like LG4F, who I got the route from, spread the word about great methods like this. FeelsGoodMan Clap.

So, you wanna become the richest Space Uber in the galaxy? Good. The first thing you need to do is obtain a good ship to get it done. The goal is to fit as many Economy Passenger Cabins in your ship as possible. In my experience, the Type 6 is a good starter ship. Try using a fit like this, which will cost around 1.7 million credits. Please note, this build is flexible and if you're strapped for credits, you can lose the shield boosters, chaff, and downgrade the FSD (Frame shift drive). Otherwise, this will get you started with 50 economy passengers. That may not sound like much, but you'll see in a bit why it's perfectly fine SmileFaceNoSpace.

The next thing you need to do is to head over to Belis (Tombaugh Platform). This is where a bulk of your work will take place. If you want travel to Belis in a ship with good jump range, you can use whatever you want to get there, and then purchase a Type 6 with cabins at Krinda (Xiaoguan Station). The basic order of operations is this:

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Build Reputation

The easiest and most efficient way to build reputation at this station, is to stack "Data delivery" missions. To do these missions, you need a ship that is able to land on a medium landing pad (meaning no large ships). The awesome thing about Belis is, these mission will have the same destination. (Mimuthi) Look for missions with the name "Boom Data Delivery", "Internal Report Delivery", or "Courier Job Available". All of these missions require no cargo capacity which makes them easily stackable. When choosing a mission, be aware of the mission rewards which may include commodities. If they do, you must have the required cargo capacity to complete the mission. I recommend you have at least 8 tons of cargo space in your mission ship.

Stack these missions until the system tells you cannot take any more. To stack missions, simply switch between SOLO and PRIVATE modes in the Elite: Dangerous menu. It is also worth mentioning that if you see a donation mission for these factions, take it immediately! Don't worry about those credits as you'll make them back ten fold! Congratulations, you've completed the hardest part of all of this.

Gather Passengers

Now that you have the appropriate reputation with the factions (at least Friendly), they should be offering you passenger delivery missions to Haiden. Why Haiden? Because the station is 500k+ LS from the star, and people pay good money for that. If you don't see any delivery missions to Haiden, flip the mission board until you do. This could take 15 to 30 minutes for most people, so be patient. You don't have to fill your entire passenger cabins to proceed. It is usually good enough if you fill 80% or more. Keep your eye on the mission timers because it is quite possible to run out of time while flipping the mission board!

NOTE: If the controlling faction's state isn't BOOM, you'll notice less passenger missions. It's best to do this when the state is BOOM.

Bask in the glory of credits

Opulence. You has it. Deliver these wonderful folks to Haiden, and then take a lap in your swimming pool full of credits. Now that you have these credits, you should reinvest and make even more opulenceses. My suggestion is to upgrade the Type 6 to a Type 7. Here is a Type 7 build that you may like. Once you've outgrown the Type 7, go ahead and find yourself a solid gold Anaconda for supreme opulence.

Note, Belis isn't the best location for passenger missions. Once you get the hang of this method, feel free to fly over to Upsilon Aquarii (Allen Hub) and deliver passengers to LTT 9360 (Smeaton Orbital). It's 1.8 million LS to the station, but you'll probably make 3 times more credits. SUPREME OPULENCE.

See you space cowboy.

Update 01/13/2018 - Note that the Allen Hub -> Smeaton Orbital run directly affects the Black Bird Consilium player faction. An alternate route would be at MEDB. Pick up passengers at Corycia (Large Orbital Pad), Parutis (Large Orbital Pad), or EEA (Medium Orbital, Large Planetary Pad) for even more opulence. I have tested the Corycia origin. Have fun!